In my experience, merged conversations are a mixed bag. It’s nice to not have to hop back and forth between two strings for the same person. However, the conversation can get somewhat disjointed. Especially if that person doesn’t use Hangouts much on their mobile device. You can, fortunately, un-merge a specific conversation. Touch the menu button at the top right and select Un-merge SMS. Then, the conversations will break apart into two separate strings.
